The invention relates to a method and a device for generating compressed air and blowing it into an internal combustion engine, in particular a diesel engine, having an exhaust gas turbocharger.
Such internal combustion engines, for example piston engines such as diesel engines, with an exhaust gas turbocharger have, for example, an operating state during acceleration which is referred to as “turbo lag”. Here, when the throttle is opened the internal combustion engine does not react with an increase in the rotational speed until after a certain delay time during which exhaust gas energy is not available, i.e., is sufficient exhaust gas pressure is not available to drive the exhaust gas turbocharger, and therefore no compressed fresh gas is available. In order to get around this “turbo lag”, solutions have been proposed which are described in laid-open German patent applications DE 10 2006 008 783 A1 and DE 10 2006 785 A1. In said documents, compressed air, for example from a compressed air accumulator, is introduced into the intake line of the internal combustion engine in a controlled fashion in order to cover the fresh gas demand of the internal combustion engine when said demand is increased. This is carried out by a component which is arranged in the intake line between the compressor of the turbocharger and the intake manifold and which has a compressed air port and a controlled flap. When compressed air is fed in, the controlled flap is closed, with the result that the compressed air does not flow into the compressor of the exhaust gas turbocharger but rather flows directed into the intake line.
In engines with exhaust gas circulation, it is in addition desirable that sufficient fresh air is still fed to the engine in addition to the exhaust gas in order to avoid putting the dynamics of the engine at risk. Here too, the exhaust gas turbocharger is capable of feeding sufficient fresh air only if it is operated by a sufficient flow of exhaust gas. The active blowing in of air is also capable of contributing significantly to improving the engine dynamics here.
The compressed air which is necessary for the blowing in of air can be made available by a compressed air brake system in vehicles with such a system, for example in a separate compressed air vessel which is separate from the brake system.
The blowing in of air in the case of vehicles which do not carry any compressed air with them is problematic.
The engine itself can be configured as a compressed air generator, which is the state of the art today. Systems are known which selectively do not supply certain cylinders with fuel on a temporary basis and which carry away the air which has been compressed by the piston in this way into a reservoir vessel.
The object of the present invention is therefore to make available a method and a device for generating compressed air and blowing it into an internal combustion engine in which the above disadvantages are eliminated or significantly reduced and further advantages are obtained.
A basic idea of the invention is to make a system combination which is generated during operation of the internal combustion engine without combustion and using this compressed air, which is then stored and used again in a subsequent combustion mode for a more rapid increase in pressure in an intake cycle.
This advantageously ensures that an over-run fuel cutoff mode of a motor vehicle is utilized to thereby generate compressed air. This is particularly advantageous when a compressed air brake system with all its components is not present.
In the over-run fuel cutoff mode, which can be clearly determined from the operating parameters of sensors which are frequently already present in the vehicle or an engine controller which is present, compressed air is generated by at least one cylinder of the internal combustion engine to which fuel is not fed in the operating state without combustion. This can only be a single cylinder which is provided, for example, particularly for generating pressure and which can be added to the circuit as an additional cylinder only when the internal combustion engine is subjected to high loading. However, it is also possible for all the cylinders to jointly compress only intake air without fuel, and said air can then be extracted from a common exhaust line via a controlled valve, in this case, the exhaust line can be constricted in cross section by suitable means, for example a throttle valve (in the FIGURE, valve 29 in the flow path of exhaust gas outlet 8) such as an engine brake, in order to achieve a greater air quantity yield.
The valve is controlled by a control unit which interacts with the engine controller or sensors in order to open this extraction valve at the correct time, which extraction valve then, when in the opened state, produces a connection to a compressed air vessel in which the extracted, generated compressed air is stored. The valve can also be connected only when there is one cylinder and/or with all the cylinders, in order to obtain a large possibility of variation in the quantities of generated and stored compressed air.
The stored air is available for the controlled blowing into the next acceleration process of the internal combustion engine. As long as all the cylinders of the internal combustion engine are used to generate compressed air, even brief over-run fuel cutoff phases of the vehicle in which the internal combustion engine is installed may already be sufficient to generate sufficient quantities of compressed air for the blowing-in process.
In a repeating operating mode, that is to say over-run fuel cutoff phases are followed by acceleration phases, and vice versa, the storage of the compressed air is necessary only for a brief time. Here, it is not required of the compressed air generating means that it must always make available sufficient compressed air, as is the case, for example, in a compressed air brake system. Specifically, the storage of the compressed air for the blowing in of air does not have to be made as complex for only a brief storage time as the storage of compressed air in a compressed air brake system. In particular, it is possible to dispense with the drying of air as long as the condensation water which is produced is discharged from the reservoir vessel, for example by a water separator. The internal combustion engine can advantageously basically be supplied with non-dried air.
In a further embodiment, the gas feed device is a fresh gas line section of a device for supplying fresh air for the controlled blowing in of compressed air. Here, a combination of the advantages of the blowing in of compressed air in terms of what is referred to as “turbo lag” as well as those of improved exhaust gas circulation are obtained.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings.